Manufacture of midsoles



i Patented Aug. 9, 1938 UNITED STATES PATENT OFFICE MANUFACTURE OF MID-SOLES No Drawing. Application February 4, 1935, Serial No. 4,879

5 Claims.

This invention relates to the manufacture or preparation of midsoles or midsole material of the type comprising felted fibres associated with a bonding medium. The midsole material of the present invention is adapted for use in the manufacture of shoes, being used as a substitute for part of the thickness of the leather ordinarily used for the outer sole.

It is common practice, in the manufacture of certain types of shoes, to substitute for a portion of the outer sole, a layer of fibre board made from hard beaten rag or kraft fibre or, in other cases, a layer of fibre board may be used to reinforce a relatively thin outer sole to yield a composite sole of greater thickness. This fibre board may or may not be saturated with asphaltic or resinous binder materials, depending upon the characteristics of the particular fibre used in its fabrication. These products are not entirely satisfactory as they are too stiff to make a flexible, composite sole for a shoe; do not sew satisfactorily; tend to delaminate or crack during the service life of the shoe; or are adversely alfected by water during the flexing and distortion of the shoe sole during service.

The product of this invention, to a large extent, overcomes the deficiencies and imperfections of the prior art materials used for midsole in that it has high flexibility, extreme toughness, great durability, continuous high water resistance during its life, and is capable of being worked and sewed in a manner more closely akin to leather than the previous materials. It also has the advantage of yielding a cut edge which is cleaner from loose fibre than the previous untreated fibre board midsoles, and does not show the smeariness due to exudation of the binder charac-j teristic of asphaltor resin-saturated midsolesi As a matter of fact, it has been demonstrated that the product of this invention can be cut and trimmed very easily and very satisfactorily in large scale continuous production in shoe factories to give an attractive exposed edge, without gumming or dulling the knives to the extent that prior art materials did. In short, this material is a better leather substitute than prior art midsole materials because it more closely simulates the characteristics of leather.

The product of this invention consists of a felted fibrous product suitable for use as a midsole, having the characteristics of having been made by the wet web saturation process such as described in my United States Patent No. 1,966,458, comprising a base of vegetable or other paper making fibre, the finished material being of laminated or wet machine construction, containing approximately 15 to %-ofrubber.. and.v

5% to 10% of a1uminum soap; having a density of foufte'htlfs to six tenths ounce per cubic inch, a hydrostatic resistance in excess of 60 pounds per iron on a standard Mullen tester; capable of taking at least seven stitches per inch on a standard shoe sole sewing machine without the thread pulling through, and possessing the characteristic of cutting easily and smoothly without gumming cutting knives.

The following example is given by way of illustration to show one way of manufacturing the product of this invention. While this example represents the preferred method of carrying out this invention, it should not be construed as limiting the scope of the invention. It will be aparent to one skilled in the art that many variations may be made from the example without departing from the spirit of the invention.

Five hundred pounds of cut cotton rags are furnished to a regulation paper beater and are beaten with water at a consistency of 4 to 5% for a period of 4 to 8 hours or until the slowness of the beaten fibre reaches a predetermined value which is known to yield a wet water-laid web which will be susceptible to rapid and thorough saturation by aqueous saturating media under the conditions encountered in the saturating machine, which conditions are described in wet machine type of saturation, see for instance, my Patent No. 1,966,458. When the fibre has been beaten to this degree of slowness, fifty pounds of ordinary soap are added to the beater in the form of an aqueous solution. While it is preferred to add the soap in the form of an aqueous solution, it is equally advantageous to add this ingredient as solid soap or any other form in which it is available. After admixture of the soap and beaten fibre, sufficient alum (aluminum sulfate) is added to the beater to precipitate the soap as a water-insoluble film and bringthe beater contents to a pH of 5 or less. The alum may be added as dry powder, aqueous solution or in any other convenient form.

A web of the conditioned fibres is then formed on a suitable Fourdrinier or cylinder machine to a thickness of about 8 to 12 thousandths of an inch as measured on the web issuing from the press rolls; at this point the wet web should contain 55% or less of water. It is then passed through a wet web saturating machine containing a suitable latex or aqueous rubber dispersion having 20% to 25% rubber solids concentration, stabilized with sodium silicate and compounded with rubber anti-oxidant, such as beta naphthylamine, and a fungus preventative such as beta napthol, zinc salicylate or the like.

The conditions prevailing at the make-up roll of this machine are such with respect to pressure and peripheral speed that the incoming webs are sealed to those already formed on the roll, yielding a sheet which contains the desired quantity of rubber, which should be approximately of the total weight of the sheet. When a sufficient number of webs have been plied in this manner, the sheet is stripped from the roll with an awl in the customary manner for removing wet machine board, and is dried at a temperature not exceeding 180 Fahrenheit in accordance with standard fibre board practice as is well known to one skilled in the art, preferably in a toggle drier. The dry sheet then contains the rubber in a continuous film surrounding the fibres, according to the description previously given in U. S. Patent No. 1,966,458.

On removal from the drier the sheets are compressed to smooth and compact the surface. This may be accomplished by pressing between the platens of a press or passage between calender rolls. The press platens or calender rolls may be either hot or cold. The preferred method is to pass the sheets between hot calender rolls. Cold calendering is not as effective in fluxing the soap near the surface as hot calendering, and is not as effective in improving the finish and hydrostatic resistance as hot calendering. The compacted sheet is then trimmed and is ready for cutting midsoles therefrom.

In a 3 iron sheet of approximately 70-75 thousandths inch in thickness, the weight per square yard is approximately 3 pounds; the hydrostatic resistance in a Mullen tester containing water, and from which the rubber diaphragm has been removed, is 200 pounds per square inch or more. The bursting strength of the dry sheet is in excess of 400 pounds per square inch, and the material is capable of being sewed in a standard shoe sole sewing machine, inserting at least seven stitches per inch without stitches pulling through or breaking of the material intermediate of the stitches. It will hold shoe nails and can be cut and handled in a satisfactory manner in the manufacture of shoes. It presents a smooth, non-fuzzy edge, due to its good cutting qualities, and does not gum or dirty the knives used in cutting even at the very high speeds when the knives become quite hot. It is decidedly leathery in feel and handling because of its high flexibility and toughness. It does not crack or break when bent double and does not delaminate on repeated sharp flexing. It is mouldable and conforms readily to an underneath surface.

Depending on the strength and toughness required, lower grade fibres may be used than the one mentioned above. For example, a mixture of rag and kraft may be used, or kraft alone, there by decreasing the cost and to some extent the flexibility, durability and strength of the product; or higher grade fibres may be used, such as linen and rope, giving increased toughness; also leather fibres, wool, hair and the like may be used for their specific effect on the properties of the finished midsole. The percentage of rubber, which may be either from latex or artificial aqueous rubber dispersions, may be varied within relatively wide limits, also varying the degree of flexibility in proportion to the amount of rubber used.

The proportion of soap may be varied, thus increasing or decreasing the water resistance or wet hydrostatic resistance, smoothness of surface, and smoothness of edge out of the finished material. Suitable types of pigments may be incorporated either in the heater or in the saturant to give the desired color to the finished material. For example, in black and brown it is preferred to introduce the color in the form of a direct dye in the beater, whereas in the case of white it is preferred to add pigments to the beater and to the saturating fluid.

The purpose of introducing rubber into a rag composition as above described, which represents one of the types of fibre used in previous midsole material, is to toughen the fibre structure and give it increased flexibility and resistance to tear.

Another point of difference from the all fibre midsole, or fibre board previously used as a midsole, is that whereas the strength and flexibility of the old midsole was obtained by the use of hard beaten fibres, the fibres used in this method are merely smoothed out and refined, are not highly hydrated, and would not of themselves have the binding qualities of a highly hydrated fibre, or produce a hard, strong board. The needed binder, however, is added in the form of a continuous film of rubber introduced by saturation of the wet web, and the combination of relatively soft fibres and rubber binder, producing the flexible, tough, resilient product of this invention. This method provides the improved leather-like quality evident over the previous unsaturated, highly hydrated fibre midsole.

The use of a non-highly hydrated fibrous base retains the long fibres in the base which are necessary to impart toughness to the sheet, permitting continual fiexing of the midsole to take place during use without cracking or breaking down whereas, in the old type of midsole made by highly hydrating the fibres, there was danger of the continuous flexing causing the midsole to crack.

It is to be understood that I may use rubber or rubber substitutes and that the term rubber is intended to include all rubber substitutes such as the material commercially known as Duprene, Chloroprene, Thiokol, rubber phenolic resins, modified glyptols, and the like.

As previously stated, one of the disadvantages of the old type unsaturated fibre midsole was its stiffness which made it undesirable to use more than say 10% to 20% of the entire sole thickness of the fibre board, as otherwise the stiffness of the fibre board would overcome the normal flexibility of the leather and would result in an uncomfortably stifi sole which was susceptible to cracking. This new type with its much greater flexibility makes it possible to use proportions up to one-half, or possibly more, of the entire thickness of the sole of the midsole, which effects a considerable economy to the shoe manufacturer without undue stiffening of the entire sole and without danger of cracking of the midsole because of flexing.

I claim as my invention:

1. A leather substitute for use as a midsole com prising a felted fibrous product exhibiting a relatively low degree of fiber hydration of wet machine-laminated construction associated with a bonding medium consisting essentially of approximately 15% to rubber and containing approximately 5% to 10% water-insoluble soap, by weight, the rubber being present as a continuous film surrounding the fibres and the product possessing the characteristics of having had the rubber incorporated by saturation of a wet fibrous web.

2. A leather substitute for use as a midsole comprising a felted, fibrous product exhibiting a relatively low degree of fiber hydration of wet machine-laminated construction containing approximately 15% to 35% rubber by weight, and approximately towater-insoluble soap, by Weight, the rubber being present as a continuous film surrounding the fibres and the product possessing the characteristics of having had the rubber incorporated by saturation of a wet fibrous Web and of cutting easily and smoothly without gumming cutting knives, and exhibiting a continuous high water-resistance, during flexing and distortion of the midsole in service.

3. A leather substitute for use as a midsole comprising a felted fibrous product exhibiting a relatively low degree of fiber hydration of wet machine-laminated construction associated with a bonding medium consisting essentially of approximately to 35% rubber and containing approximately 5% to 10% water-insoluble soap, by weight, the rubber being present as a continuous film surrounding the fibres and the product possessing the characteristics of having had the rubber incorporated by saturation of a wet fibrous web and of cutting easily and smoothly without gumming cutting knives, and exhibiting a continuous high water-resistance, during flexing and distortion of the midsole in service, and having a density of .4 to .6 ounce per cubic inch.

4. A leather substitute for use as a midsole comprising a felted fibrous product exhibiting a relatively low degree of fiber hydration of wet machine-laminated construction associated with a bonding medium consisting essentially of approximately 15% to 35% rubber and containing approximately 5% to 10% water-insoluble soap, by weight, the rubber being present as a continuous film surrounding the fibres and the product possessing the characteristics of having had the rubber incorporated by saturation of a wet fibrous web and of cutting easily and smoothly without gumming cutting knives, and exhibiting a continuous high water-resistance, during flexing and distortion of the midsole in service, and having a hydrostatic resistance in excess of 60 pounds per iron.

5. A leather substitute for use as a midsole comprising a felted fibrous product exhibiting a relatively low degree of fiber hydration of wet machine-laminated construction associated with a bonding medium consisting essentially of approximately 15% to 35% rubber and containing approximately 5% to 10% water-insoluble soap, by weight, the rubber being present as a continuous film surrounding the fibres and the product possessing the characteristics of having had the rubber incorporated by saturation of a. wet fibrous web and of cutting easily and smoothly without gumming cutting knives, and exhibiting a continuous high water-resistance, during flexing and distortion of the midsole in service, and capable of taking at least seven stitches per inch on a standard shoe sole sewing machine without the thread pulling through or breaking of the material intermediate the stitches.

IZADOR J. NOVAK. 

